High-frequency potential dividing termination



' 1949- H. J. TYZZER ,476

HIGH-FREQUENCY POTENTIAL DIVIDING TERMINATION F-iled May 26, 1944 HOWARDJ. TYZZER INVENTOR ATTORN EY Patented Feb. 1, 1949 HIGH-FREQUENCY,POTENTIAL DIVIDING TERlVlINATION' Howard J. Tyzzer, Caldwell,

N. J., assignor to Ferris Instrument Laboratories, Boonton, N. J

a corporation of New Jersey A ueatmn May 26, 1944, Serial No.- 537,509Claims. (01. 178-44) My present invention broadly relates to dividingelectrical potentials into lower potentials, and more specifically to sodividing such potential developed by electrical alternating currents.

An object of my present invention is to divide potential developed atthe output end of a line or cable employed to transmit electricalalternating currents where certain technological reasons in casesof'such transmission require that the line or cable be terminated in animpedance substantially equal to the characteristic or surge impedanceof the said line or cable, in connection with which preserving theeffects of the specific form of output termination is essential.

1 One particular object of my present'inven'tion is to make iteffectively usable with a terminated signal generator output cablehaving the attributes disclosed in Ferris Patent 2,265,637 of December9, 1941, including in particular the substantially uniform distributionof its inductance and capacitance attribute disclosed thereby.

A particular service renderable by such a terminated cable signalgenerator is the one of using the alternating potentials developed inits output termination element, which potentials are d,- rived from theelectrical alternating currents generatedwithin the signal generator, todependably check and determine the electrical alternating potential,responsive characteristics of devices, such as radio receivers, as .fastas built in order to be certain that the respective unit building ofsuch devices has closely followed the responsive objectives of thespecific design and/or model of thesame. This service now has to coverchecking responsiveness to electrical alternating current potentialsranging in frequency from fractions of a megacycle to ultra highfrequencies represented by hundreds of megacycles in respectivecomprehensive bands of frequenc-ies in accordance with the respectiveservices the respective devices are designed to render.

As the frequencies of the electrical alternating currents with which onehas to deal in the cases of these practices increase, the matter ofmaintaining dependability within reasonable tolerances becomes more andmore stringent, with the result that what proved to be satisfactory ayear or so ago fails to measure up to present day requirements. Theshorter the signal generator output cable of the Ferris patent,supra,'can be, the less stringent is the matter of maintaining thedesired dependability, but because of the usual Work bench conditionsthat must be taken into:

consideration in the fast use that goes on in doing said checking ofperformances, nothing less than a 15-foot long output cable has so farbeen ofiered to the public. Accordingly, in those cases that have arisenof the stringencies having to do with maintaining dependability ofresults as the demands for such services at higher and higher ultra highfrequencies have acceleratedhnding the answers for the same byshortening the output cable has been frowned upon.

The object of the Ferris patent, supra, in its terminating of the signalgenerator output cable is the one of minimizing the development thereinof undesirable reflections or the energyitranse mitted to the terminatinimpedance'common to improperly terminated output elements, the need forwhich becomes more and more essential as thefrequencies of the nowgrowing more common uses of ultra high frequencies are increased, so

that it'has becomedecidedly more important to 7 do nothing upsetting tothe said proper termination in making use of the signal generatorsinvolved.

In using terminated lines or cables, and especially in those usescalling for signal generators, it often happens that the total outputpotential across the usual terminating resistor is either not wanted orcan be helpfully reduced in the case of the particular work on hand, inWhich'cases it is all important to effectively maintain propertermination irrespective of the particular connections made to obtainthe reduced potential It is this object to which my present invention isdirected, the necessary substance of which is here inafter describedwith the aid of the single illus-,

comprising closely spaced double conductors consisting of the lineelement C centered in a conductive sheathing G2, the former beingequipped with a flexible insulating covering.

across indicated difference of potential points of an indicatedresistance potentiometer P in cir-' cuit with an indicated generator ofelectrical alternating currents, A. C., which, in all signal generatorcases would be of the usual vacuum tube and Circuit type, and may havein circuit therewith the indicated modulator M in case a modulatedelectrical alternating current is needed or desired, with it beingindicated by the arrow that the frequency of electrical, alternatingcurrent These two conducting mediums are respectively connected"generation is variable. These elements are all located at the input endof the cable involved.

The output end of the cableis indicated as being generally terminated ina block B which will be fully described further along in thisdescription. The conductors C and G2 per se are indicated as terminatedin terminals HI and GT, respectively, having a resistance element R4interposed therebetween. A third terminal LO has interposed between itand terminal HI a resistance element R and an inductance element L inthe order named, and between it and terminal GT are connected threeresistance elements RI, R2 and R3 in paralleled relation.

The block B is of conductive material, preferably aluminum, ments R4, R,L, Rl, R2 and R3 in appropriately configured recesses extending into thebody thereof from the bottom which preferably has a bottom cover made ofan appropriately shaped sheet of the same material. The recessedelements may all be of self-insulating types.

The terminals HI and LO are of conductive material set in holes spectivelocations of the block B indicated as fitted with insulated bushings,with the respective connections therefrom to conductor C and the otherelements involved being made, as by soldering, before the bottom isclosed. Terminal GT, however, is given a conductive relation to block Bin order to be maintained in conductive relation to the outer end ofconductor G2 through the body of block B as indicated by the broken lineGl. The broken line G3 indicates thatthe input end of the conductor G2begins at one end of the potentiometer P; the housing H indicates thatthe AC generator is preferably isolated from the output cable and anydevice being checked, which necessitates a housing of effectiveshielding such as is aluminum; and the arrow A indicates that the valueof the potential of the electrical alternating current supplied to thecable is controllable.

In quantity production of signal generators, common sense dictates theadoption of a construction of output cable that can be depended upon tohave in the particular length adopted a substantially uniformcharacteristic or surge impedance in order that proper uniformtermination may be had in resistors of the right ohmage of standardconstruction. For the purpose of giving details of as to how to apply mypresent invention to quantity production of signal generators I adopt acharacteristic or surge impedance of 30 ohms for the output cable astypical.

Referring to the drawings, if a device to be checked for ascertainingits performance characteristics has its input leads connected toterminals HI and GT, respectively, this choice including terminal HImeans that the highest available output potentials are to thereby bebrought to bear for the particular checking involved; where as, if suchinput leads are connected to terminals L and GT, respectively, thischoice including terminal LO means that some lower order of availableoutput potentials are to' thereby be brought to bear for the particularchecking involved. In this connection, I confine my treatment of thelower order of potentials involved to a connection because thispercentage has been found to be a reduction in working output potentialscases of checking the performances of devices calling for lesserpotentials than the higher pomost suitable to general needs in the thickenough to house the ele- V drilled in the indicated retentialsconsidered for so long to be low enough for all checking.

This making of connections for such lower potentials has the advantageof causing less upsetting of the proper termination of the output cablethat unavoidably arises out of bringing to to bear the load of the inputof any device connected to the terminals for checking on the vitaloutput cable proper termination calculations because it is clearlyapparent that the upsetting reactions thus introduced into theterminating impedance are thereby reduced to about 10% of what theywould be if the connections were made to terminals HI and GT,respectively, for highest potentials; Also, because of such connectionsfor low potentials limiting thepickup ability of the input leads of anydevice being checked, the operation is automatically made lesssusceptible to pickups of extraneous signal generator leakage fields andfields of other sources that may be due to other electrical activitiesbeyond control.

Heretofore, such output cables have been.

limited for termination to two terminals; such as HI and GT, havinginterposed therebetween, as shown by R4, a resistor selected to be aspure a resistance as modern construction will permit having a resistanceohmage value substantially matching the ohmage value of thecharacteristic or surge impedance of the cable it terminates,

but to make the practice of my invention applicable to a 30 ohm cable,for 30 ohms for resistor R4. 7

As shown, the resistances Rl, R2 and R3 interposed between the L0 and GTterminals are connected. in parallel, and with each of them having aresistance they, in their paralleled relation, collectively ofler aresistance ohmage value of the order of 3.3. However, even though theseunits are selected to have in their way of being made up a minimum ofinherent inductance, and are connected in parallel to minimize theircombined inductive efiect, the residual inductive reactance resultingtherefrom, particularly at frequencies of the order of 200 megacycles inwhich I am particularly interested, is suihcient to actual workingimpedance appreciably more than their pure resistance of the order of3.3 ohms in participating in the proper output cable termination for thepurposes involved. 7

Because of output cable designing on the basis of making available 10%of the total output voltage for connections to the LO andGT terminals,it is obvious that in order for this to be accomplished the leg of thenetwork comprising resistance R and inductance L in series must havenine times the impedance established between terminals L0 and GT. Withthe resistance ohmage of R made 30 ohms, I bring about the obtaininentof the required impedance ratio of 9 to 1 by giving to inductance L suchan inductive value that combined with the inherent inductive value ofresistance R this procedure requirement is satisfied. Although thisbrings about a pure resistance of about 38.3 ohms in parallel with theohms of Rt, the increase of impedance.

due to the inherent inductance of the resistance elements added to thatof the resultant impedance so that it, in parallel with the 60 ohms ofR4, brings the total load of termination of involved down and closely tothe 30 ohms of impedance at ultra high frequencies,. the correct. matchof impedance for the particular cable. It a I substitute 60 ohms ohmagevalue of 10 ohms' make their consequential inductance L makes J farabove 33.3 ohms the output cable a those imposed by the scope them fromupsetting damage, they are kept from effectively radiating interferingcomponents of the electrical energy with which they are necessarilyactivated.

While I have made known the nature of my present invention in certainconfined respects, it is apparent that modifications may be made, andthat no limitations are intended other than of the appended claims.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is as follows:

1. In an electrical system for transmitting electrical alternatingcurrents for the purpose of remotely developing ing potentials fromwhich to abstract working therewith electrical alternat potentialsconsiderably lower in value, in which i:

system the frequencies are so high that the inherentj distributedinductances of the potentialdeveloping elements necessary thereto .mustbe taken into account in order-that the developed working potentials maybe sufficiently dependable for said purpose; the combination of a doubleconductor transmission line terminated by an impedance that remainssubstantially equal to the characteristic impedance of said line whichalso has substantially uniform distribution of its inductance andcapacitance, said impedance comprising a resistor interposed between theterminating ends of said line having an ohmage value materially inexcess of the ohmage value of said characteristic impedance of saidline, a multiplicity of paralleled resistances having appreciableinherent inductance at the operating frequencies interposed between theterminating end of one of said conductors and a terminal, and

- a resistance interposed in series with an inductance element betweensaid terminal and the terminating end of the other one of saidconductors, the resultant inductance of said inductance element and anyinherent inductance in said series-connected resistance bearing substan-40 ment is of tially the same ratio to the resultant inherent inductanceof said parallel resistances as the ratio of said series-connectedresistance to the resultant resistance of said paralleled resistances,and the summed up impedance of said paralleled resistances and theresistance in series with the inductance element being such that inparallel with the resistance interposed between the terminating ends ofsaid conductors it establishes an impedance therebetween approximatelyequal to said characteristic impedance of said line, whereby thepotentials developed across said paralleled resistances can be put towork without materially upsetting the required termination of saidtransmission line.

2. The system of claim 1, in which the ohmage value of the resistanceinterposed between the terminating ends of the conductors issubstantially double the ohmage value of the characteristic impedance ofthe transmission line.

3. The system of claim 1, in which the ohmage value :of the resistancein series with the inductance element is substantially equal to theohmage value of the characteristic impedance of the transmission line.

4. The system of claim 1, in which the in parallel impedance of theparalleled resistances is substantially equal to one-tenth of the totalimpedance arising from the in parallel impedance of the paralleledresistances plus the impedance of the in series resistance andinductance.

5. The system of claim 1, in which the characteristic impedance of thetransmission line is of the :order of 30 ohms, the resistance of theresistance interposed between the terminating ends of the conductors isof the order of 60 ohms, the in parallel resistance of the paralleledresistances is of the order of 3.3 ohms and the resistance of theresistance in series with the inductance elethe order of 30 ohms.

HOWARD J. TYZZER.

45 file of this patent:

UNITED STATES PATENTS Name Date Ferris Sept. 27, 1938 Number

